We report a straightforward strategy of accessing virtually any color in the color space through simple and predictive solution color mixing of electrochromic polymers (ECPs). Traditionally, we have utilized simple side-chain modification of a polymer backbone to broadly tune the coloration of a material either electronically or sterically. These synthetic strategies have allowed us to complete the entire color palette using dioxythiophene-based derivatives that all switch between a colored state and an achromatic, highly transmissive state in seconds or less. Because these ECPs are highly soluble, we can apply the color mixing concept used in the printing industry to fine-tune colors or recreate a specific color from just a small handful of starting ECPs.
First, we demonstrate that our primary ECPs (ECP-Cyan, ECP-Magenta, and ECP-Yellow) can be co-processed from a single solvent and follow the CMY color-mixing model. These ECP blends display the correspondingly high contrasts and rapid switching times of their blend components. Secondly, in addition to the vibrantly colored blends, we have developed a set of fast switching, high-contrast black and brown ECP blends. Given the tertiary nature of the color brown, we believe that solution color mixing of ECPs is the simplest way to access this part of the color space. Finally, we use these brown blends to demonstrate the attractiveness of ECPs as active materials in color changing eyewear. This was done by assembling fully user-controlled, high contrast, fast switching, electrochromic lenses (25 cm2) that were fabricated using roll-to-roll compatible coating methods. These lenses can be powered with a small coin cell battery, and they switch between the colored and transmissive states in less than a second.
The ability to predictably blend ECPs while retaining the performance of the blend components should broaden the scope of these polymers, not just for the development of electrochromic sunglasses and visors, but also for electrochromic window and signage applications.